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Off the grid & off the pipe…in San Francisco

Posted on | August 9, 2009 | No Comments

netzerosanfranThis is a post from Green Architecture Notes published by Feldman Architecture out in San Francisco.  It describes an energy-neutral house proposed to be constructed next year.

With all the building trends moving towards sustainability here in New York City, it is still SO MUCH more difficult to do a net-zero house here than in the Bay Area.

For one thing, our buildings are generally taller with smaller footprints so the proportion of available roof area (for renewable energy) to living area is much smaller.  Also, our winters are colder and our summers hotter and more humid so we use much more energy for heating and cooling.  Not to make excuses but a net-zero house here is kind of like the holy grail.

Given that we’re comparing climates, I thought I’d take this opportunity to introduce the concept of degree days which are a useful tool to compare climates or assess energy efficiency strategies.

There are many ways to calculate degree days.  The simplest formula is to subtract 65 degrees from the average daily temperature.  If the number is greater than zero, it is equivalent to that number of cooling degree days (CDD), if the number is less than zero, it is equivalent to that number of heating degree days (HDD).

For example.  Today’s high was 82 and low was 76.  The average temperature is 79 degrees.  79 degrees minus 65 degrees = 14 cooling degree days.  You can conveniently add them up to get monthly and seasonal totals and compare different climates or different time periods within the same climate.  

For comparison purposes, I downloaded the last 12 month’s heating degree days and cooling degree days for San Franciso and New York City from

As you can see, New York City has much higher number of heating and cooling degree days which means that a building in New York City would need to use more energy for heat and cooling to maintain the same comfort level as would a comparable building in the Bay Area.



You can also use this information to assess recent energy efficiency improvements.

You would adjust the post-improvement annual energy consumption with the pre-improvement consumption by degree days in order to compare “apples to apples”.

For example, if you are thinking that the extra insulation you added last fall didn’t work as well as you thought, it could be that we just had a colder winter so your bills were higher than you might have expected, even with the added insulation.  The chart below shows that the 08/09 winter (in green) was, in fact, colder than the 07/08 winter (shown in blue).



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Established in 1999, Ellen Honigstock Architect PC is a full-service architecture and energy auditing firm based in DUMBO, Brooklyn.

Our solutions are environmentally conscious and the criteria we use are based on national standards developed to bring long-term saving, efficiency and well-being to our clients. Over 35 years combined experience building in New York City gives us an edge in meeting tough schedules and navigating the city's complicated requirements.

About Ellen:

As the Residential Green Building Advocate for the Urban Green Council since 2007, Ellen has been promoting sustainability in the residential marketplace in NYC.

In the position of Chair of the Homes Subcommittee the NYC Greening the Codes Task Force, Ellen has been heavily involved in recommending new green policy in NYC as related to updating building codes, rules and regulations.

Ellen teaches Building Science, Building Envelope, Water Conservation, Indoor Air Quality, Quantifying Energy and Green Building Plans at the 1,000 Green Supers program for The SEIU Local 32 BJ Thomas Shortman Training Fund.

Registered Architect, NY, NJ, CT
LEED Accredited Professional
BPI Certifications:
Building Analyst
Energy Efficient Building Operator
Multi-Family Building Analyst

Ellen Honigstock, LEED AP
Ellen Honigstock Architect PC
45 Main Street #806
Brooklyn, NY 11201
(212) 228-1585


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